RHINO FOSSILS IN CALIFORNIA

The scientific analysis of any fossil records is always a “process.” Initially, it is based on 1) previous observations; then it proceeds to 2) any new data. Then, as step 3), it is then usually possible to make new interpretations. That is certainly the history of rhino fossils in California.

Previous observations. Chester Stock wrote several papers about the “earliest rhino fossils” found in California. These were conveniently summarized, in the form of sketches, of supposedly the earliest California rhinos, by Savage and Downs (1954, fig. 2).

New data. In the past few years, there have been exciting discoveries (e.g.,  through out the world, namely China and Elsmere Island (in the Arctic region of Canada). 

New interpretations. Prothero and Schoch (2002) did a detailed analysis of the fossil record of rhinos and made some very useful observations. Rhinoceros likely originated from tapir-like animals during the middle Eocene, but this transition remains controversial.  Bai et al (2020) made a significant step in our understanding of fossil rhinos. From these two papers, it is now possible to state that the first true rhino is the horse-like Hydrachyus, known from Inner Mongolia (China), Europe, and Arctic Canada (Elsmere Island). 

On the west of North America, the hippo-like, short-legged rhinoceros (no horn) Teleoceras is known from middle to late Miocene [13.5 to 7.3 mya, in the Dove Spring Formation (part of the Ricardo Group) in the El Paso Mountains of Kern County, California. About 100 intact specimens belonging to this genus are famously known from a Miocene volcanic ash-fall event in Nebraska (see Wikipedia). 

Also living on the west coast of North America was the rhino (no horn) Aphelops from the middle upper Miocene Mint Canyon Formation in the Soledad Basin of southern California. This was the last native occurrence of fossil rhinos in California.

Note: Ancestral forms of Teleoceras and Aphelops “arrived” in California via a land bridge called “Beringia 2”, [see my earlier posts on Nov. 1, 2022]. Beringia 2 occurred between 25 and 5 mya, when northeast Asia and northern Alaska were “linked” together.

Figure 1. Teleoceras fossiger Cope, 1878, from a public domain sketch by Horsfall in (1912) 1913, a renowned American wildlife illustrator. This genus was endemic to North America and is found in rocks ranging in geologic age from Miocene to Pliocene. [Note: The Los Angeles County Museum of Natural History has a skeleton of Teleoceras on display].  

Figure 2. Aphelops was also endemic to North America, and the representative fossil used here is from the upper Miocene Mint Canyon Formation in Soledad Canyon, northern Los Angeles County. Fossils of Aphelops are found in rocks ranging in geologic age from Miocene to Pliocene. My drawing is modified from an image by Jay Matternei (www.facebook.com/photo). 

Figure 3. Modern “Black Rhino” living (many years ago) at the Los Angeles County Zoo. Image via R. Squires. Today, of course, these rhinos are from Africa and elsewhere and have been imported to zoos throughout the world. 

References

Bai et al. 2020. The origin of Rhinocerotoidea and phylogeny of Ceratomorpha (Mammalia, Perissodactyla). Communications Biology. https://doi.org/10.1038/s42003-020-01205-8 pdf available online for free.

Horsfall, R. B. 1913. A public domain document available online (e.g., Wikipedia). 

Prothero, D.R. and R.M. Schoch. 2002. Horns, tusks, and flippers: The evolution of hoofed mammals. The John Hoplins University Press. Baltimore.

Savage, D.E. and T. Downs. 1954. Cenozoic land life of southern California. Chapter 6, pp. 43-58. In Geology of Southern California, Bullein 170, Chpater 3, Historical Geology. Division of Mines, San Francisco.